It is generally necessary to carry out can making in a series of separate process stages which often require different tooling. Whilst this was once achieved on an in-line conveyor system, it is now more common practice to use a series of rotating circular turrets.
U.S. Pat. No. 5,282,375 (REYNOLDS METAL COMPANY) describes a handling system for necking the open end of a metal container body, or can. The can bodies are supported on the periphery of a circular turret by means of a negative pressure, also referred to as ‘suction vacuum’ or simply ‘vacuum’. For consistency, that terminology is also adopted herein. A vacuum manifold arrangement supplies high volume low suction vacuum to a small number of locations in the vicinity of the infeed location rapidly to locate container bodies on base pads. A low volume high suction vacuum supply to the downstream spindles ensures proper clamping suction to maintain containers on the base pads during necking.
Rotary manifolds in various forms have been used for many years for the supply of compressed air to tooling. Typically, air galleries selectively communicate with supply through circumferentially equi-spaced holes in a rotating disc and slots in a stationary shoe. The air manifold of EP 1308225 B (DELAWARE CAPITAL FORMATION) uses both high pressure and low pressure recycled air. High and/or low pressure air is bled from a container so as to be re-used. This bleed back process is said to recoup about 50% of the air volume. However, the bleed back process is dependent on the effectiveness of seal between manifold and rotor. Back pressure on the pistons which are used to achieve this seal is limited to ports which are in a dead head circuit, i.e. a can sealed on the knockout. This occurs over a very small arc of the manifold. There are springs adjacent to the piston chambers which press the manifold against the rotor if no cans are present. When there is no can present, there is no dead head circuit and the springs are fairly inefficient on their own.
EP 1828035 A (CROWN PACKAGING TECHNOLOGY, INC) describes a transfer mechanism for a multi-stage die necking station. The transfer device uses conventional turrets having 3 zones, each carrying out one stage of multi-stage die necking. After completing each stage, a transfer wheel removes the can from the pocket for that stage and transfers it to the pocket for the next stage. Alternatively, the can may be transferred to a separate turret if further process stages are required. This application uses pockets to support cans around the periphery of a turret but it also suggests that this support could be achieved by suction pads.
Loading and unloading the can into the tooling using suction, vacuum and/or compressed air leads inevitably to leakage of air to the atmosphere, for example around the edges of the can and during movement of the can. As noted above with reference to EP 1308225 B (DELAWARE CAPITAL FORMATION) seals may only be achieved over a small arc of the manifold. Furthermore, this reference uses two pressure heads which require two distribution systems. This duplication of hardware consequently has substantial maintenance needs.
This invention seeks to provide a method and apparatus which overcome the problems of the prior art and which use/waste less compressed air, even in a situation when no cans are present.